I'll break it down by region:
North America: Switch by a small margin (I know this is bold, but the Switch is about to win 4 npd's in a row. If they can keep the momentum, it could happen. Plus, they have Pokemon)
Europe: PS4 by huge margin (shouldnt have to explain myself here)
Japan: Switch by a huge margin (again, shouldnt have to explain myself here either)
WW: PS4 will get 130M, while Switch will get 105M. Judging off the predictions above, it looks like a close race, but PS have a bigger audience in the rest of the world than Nintendo.
Bet with Intrinsic:
The Switch will outsell 3DS (based on VGchartz numbers), according to me, while Intrinsic thinks the opposite will hold true. One month avatar control for the loser's avatar.